how to create__r objects?..for exxample job_Application__r

Hi,  

•  "__r" is used for retrieving field values from the object related another object when those objects have a relationship via the Lookup field 
• https://developer.salesforce.com/forums/?id=906F00000008llXIAQ
• https://developer.salesforce.com/docs/atlas.en-us.soql_sosl.meta/soql_sosl/sforce_api_calls_soql_relationships_and_custom_objects.htm
• If you want to learn more about object relationships then go for it: https://trailhead.salesforce.com/content/learn/modules/data_modeling/object_relationships